Infiltration of water into snow

Measurements from a rectangular grid of thermistors set in a maritime snowpack are used to study the infiltration of water during two midwinter rain on snow events. The progress of wetting is tracked in real time by monitoring changes in the position of the zero‐degree isotherm. Rates and patterns of infiltration are calculated for each event. Infiltration was not uniform, and water penetrated through localized channels that often occupied less than 50% of the total volume of the snowpack. The evolution of wetting was strongly influenced by the snow stratigraphy. In one case the snowpack contained multiple ice layers, and vertical flow was impeded and diverted laterally for several hours at each layer. In the other case the snowpack was more homogeneous, and water concentrated in channels and penetrated to depth more rapidly. The measurements of temperature are also used to calculate the components of heat transfer within the snow during each rain event. Heat transfer in dry snow occurs primarily by conduction, and rates are relatively slow. However, introduction of liquid water results in the release of latent heat when water freezes on contact with subfreezing snow at the wetting front. The release of latent heat dominates heat transfer and has the potential to warm the snowpack rapidly. Rates of freezing needed to satisfy the heat equation are calculated. In both cases studied, less than 4% of the total influx of rainwater needed to change phase. Most of the rain remained liquid and wet the snow or drained through the snowpack.